1. Field of the Invention
This invention relates to a method of electrically contacting a recording medium, more particularly to a method of electrically contacting a recording medium of the type having a support layer at least the surface of which is electrically conductive, and a recording layer consisting of a photoconductor or a dielectric provided on said surface.
2. Description of the Prior Art
With this type of recording medium, in the case of electrically charging the surface of the recording layer, of carrying out electrostatic recording as by ion flow or by simultaneous single-line recording using a recording needle, of transferring a latent electrostatic image or toner image formed on the recording layer to another material, of transferring a latent electrostatic image to the recording layer from another material or of developing a latent electrostatic image formed on the recording layer, it is necessary to make electrical contact with the conductive layer in order to establish electrical connection with earth or an external electrical source. Also, there are other special cases when it becomes necessary to make electrical contact with the conductive layer as, for example, when it is necessary to connect the conductive layer with earth or an external electrical source in order to measure the charge potential of a photoconductive or insulating layer of the recording medium.
As methods for electrically contacting the conductive layer of the recording medium, there are known, among others, a method wherein the contact is established by peeling off the recording layer at an edge portion not used for recording an image and a method, as described in Japanese Patent Publication No. 500,394/1980, wherein a groove is formed from the surface of the recording layer into the conductive layer and a suspension containing electrically conductive particles is applied to the grooved portion so as to be exposed on the surface of the recording layer.
Although these methods provide good electrical connection, they are disadvantageous in that they require the formation of a portion for electrical contact, thus increasing the number of manufacturing processes for the recording medium and raising the cost of production. This increase in cost is not so important when the recording medium is used as a master recorded with a latent electrostatic image or toner image which is repeatedly transferred onto transfer printing materials. However, the higher cost becomes a major problem when the recording medium is to be used for recording of the final image.
In view of this cost problem, there has been devised a method of making electrical contact with the conducting layer of the recording medium by using a needle, rotating knife or toothed disk as the electrical contact means, i.e. as the electrode. In this method, the needle etc. is pressed onto the recording medium with a force large enough to cause it to pierce the recording layer and establish contact with the conductive layer.
This method is practical in that it makes it possible to establish electrical contact using a simple means without need of any processing of the recording medium in advance. It is, however, defective in that it does not permit the establishment of perfect electrical contact.
This defect results from the fact that the conductive layer of recording media currently in use is a thin layer of metal or the like formed by vacuum deposition. Particularly in the case of a transparent recording medium wherein the support layer, the conductive layer and the recording layer are all transparent, the maximum thickness that can be given to the metal or metal oxide conductive layer is some tens of angstroms. Thus when the conductive layer is pierced by a pin or the like, it is likely to tear, causing the contact between the needle and the conductive layer to be insufficient.